Many clinical situations require the reduction or complete stoppage of blood flow to some region of the patient's body. Embolic coils are one example of devices that may be used to stop undesired blood flow in situations, for example, requiring treatment of aneurysms, arteriovenous malformations, traumatic fistulae and tumor embolization. These conditions require that the blood flow through a portion of a blood vessel be stopped, for example by introducing an artificial device into the vessel to slow the flow to allow the natural clotting process form a more complete blockage.
Embolic coils are made from a bio-compatible material, such as platinum, to minimize problems associated with tissue irritation and rejection. These coils are often shaped as complex three dimensional curves that fill in portions of a blood vessel's lumen and slow blood flow therethrough. Often, polymeric fibers are added to the metallic coils to enhance the coil's thrombogenicity (i.e., its ability to cause the formation of clots).
In the treatment for an aneurysm, an embolic coil is inserted in the affected blood vessel using a catheter, and is placed within the bulging, weakened section of the blood vessel. When in place, the coil expands to its operational size and shape, and slows down the flow of blood through the weakened section. Over time, a clot forms around the embolic coil, and blood flow through the weakened section is completely blocked. Thus, failure of this weakened section is less likely and the resulting hemorrhage may be prevented.
Typical embolic coils are formed using two major steps: 1) a wire of platinum or other bio-compatible material is wound into a spring, forming what is commonly referred to as a primary coil; and 2) the primary coil is in turn wound around a mandrel having a more complex shape and is subject to high heat to yield a secondary coil. The secondary coil thus is a coiled wire of complex-shape. Subsequently, polymeric fibers may be added to the embolic coil, usually between the rings of the primary coil.